Base isolation is an alternative seismic design strategy in which the primary structures
and their internal components are uncoupled from the potentially damaging horizontal
components of an earthquake by base isolators which attenuate the transmission of
horizontal acceleration into the system. Rotating machines are among the key internal
components of many modern structures. In this study, flexible rotating machines
protected against seismic excitations by two particular types of base isolation systems,
Resilient-Friction Base Isolation (R-FBI) and Laminated Rubber Bearing (LRB), are
investigated. A comparative study is carried out to compare aseismic responses of base
isolation systems and their corresponding fixed-base ones in protecting a rotating
machine rigidly attached to a floor level or independently isolated.
Finite-element analysis techniques based on energy methods are proposed to
investigate a general complex model of the rotating system which incorporates nonuniform
properties as well as one or more rigid disks along the length of the flexible shaft
and complicated bearing support systems. The equations of motion for the rotating
machines using these methods are developed. An approximate linear analysis to gain
insight into the behavior of a simple linear two-degree-of-freedom isolated structure is
presented. This elementary analysis allows us to develop an analytical expression for the
fundamental frequencies, and their corresponding mode shapes, amplification factors and
design response spectra of base shear. It also demonstrates that the transmission of
ground motion to the systems is effectively controlled through the isolation of the system
at its base. The combined rotating machine-isolator; rotating machine-structure-isolator;
and structure-isolator systems, and their corresponding fixed-base ones are investigated
and compared. The governing equations of motion and the criteria of phase transition (R-FBI only) are presented. Parametric studies to examine the sample response and response
spectra, as well as effects of variations in some system properties including friction
coefficient, damping ratio, mass ratio, ground motion excitation intensity, shaft
flexibility, bearing rigidity and rotating speed, on the response of these systems are
performed. The peak accelerations and relative displacements of the base isolated
systems and corresponding fix-base ones are analyzed and compared. Other response
quantities of special interest such as sliding displacement, residual displacement,
cumulative displacement and relative-to-ground displacement of the structure are also
evaluated. Based on the numerical results, conclusions of the effectiveness of the R-FBI
and LRB systems in protecting the rotating machines and the structures are made. / Graduation date: 1998
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/33770 |
| Date | 18 March 1998 |
| Creators | Su, Wen-Chyi |
| Contributors | Yim, Solomon C. S. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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